The invention relates to a process for compensating a phase and amplitude response between a multiphase setpoint and actual value and circuit for implementing the process.
Specifying a command variable W, for example in accordance with a timing function W(t)=W sin (.alpha.t) on a known control loop consisting of setpoint adjuster, comparator, controller, controlled system and measuring transducer produces in the controlled variable a phase and amplitude shift in relation to the command variable W. With increasing frequency of the command variable W, the phase and amplitude response varies between setpoint and actual value. An undesired phase and amplitude response between setpoint and actual value is also produced in the case of multiphase control loops. A multiphase control loop represents, for example, a conventional current control for a three-phase current drive with voltage-controlled convertor. The amplitude and phase of actual value can be measured or determined without distortion in this multiphase control loop.
The phase and amplitude response is determined by the response characteristic of the control loop. If this response characteristic is known, the phase and amplitude response of the control loop can be compensated by a correction device in the command channel. If, by contrast, the response characteristic of the controlled system is a function of the disturbance variable or dependent on controlled variables which are not known or cannot be measured, the said type of phase and amplitude response can be compensated only insufficiently by means of a correction device in the command channel.
The textbook "Stromrichter zur Drehzahlsteuerung von Drehfeldmaschinen" (Static convertors for speed control of polyphase machines), Part III, Convertors, by Erich Eder, 1975, pages 102 to 111 discloses resolvers by means of which a two-phase system having two orthogonal currents is formed from a three-phase system. A current vector which rotates can be formed from these two orthogonal currents. The modulus of this current vector and the rotary angle are formed by means of a C/P transformer (Cartesian/polar).